This invention relates generally to systems for recording and playing back video signals, and, more particularly, to recording systems in which a video signal can be played back in a stop-motion fashion, with accompanying audio.
Systems of this type are particularly useful in recording and playing back video signals on video discs, in which the signals are recorded in a succession of substantially circular and concentric recording tracks, each track recording an individual video frame. During playback, selected recording tracks are scanned in a repeated fashion, to display the video frames recorded on them in a stop-motion fashion, while accompanied by playback of corresponding audio signals.
One prior system of this particular type is disclosed in a copending and commonly-assigned application for U.S. patent, Ser. No. 066,620, filed Aug. 15, 1979 in the name of W. R. Dakin and entitled "Video Recording Medium for Stop-Motion Playback", now abandoned. In the system disclosed, discrete segments of an analog audio signal are digitized and compressed in time and recorded on alternate tracks of a video disc, and corresponding frames of a video signal are recorded on the interleaved tracks. During playback of the disc, a selected audio recording track is first scanned, to recover the recorded digital audio data and store the data in a memory. The track for recording the corresponding video frame is then scanned in a repeated fashion, to produce a stop-motion display of the recorded frame, while the stored audio data is extracted from the memory and converted back to its original analog format for simultaneous playback at its original speed.
Although the recording and playback system disclosed in the aforementioned application is effective in recording and playing back a video signal in a stop-motion fashion with accompanying audio, it has not proven entirely satisfactory. This is primarily due to the fact that during playback, while scanning a track recording the digital, time-compressed audio signal, no video picture is displayed on the playback monitor. Although this occurs for only a relatively short duration, it can nevertheless sometimes be objectionable.
It therefore will be appreciated that a need has existed for a system for recording and playing back a video signal in a stop-motion fashion with accompanying audio, in which a video picture is displayed continuously on a playback monitor, i.e., without periodic dropouts. The present invention fulfills this need.